Induction-motor.



G. E. LORD.

- Patented May 9,1911 1 ninrrnn srnrns rernnr enrich.

CHARLES E. LORD, OF MILWAUKEE, VIISCONSIN, ASSIGNOR COMPANY, A CORPORATION OF NEW;JERSEY.

TO ALLIS-CHALMERS INDUCTION-Moron.

conceal Specification of Letters Patent.

rat-eaten May a, rear.

To all whom it may concern:

Bc'it known that I, Crmunns E.- 1101), a citizen of the United States, residing at Milwaukee, in the county of lVlilwaukee and State of \Visconsin, liaveinvented certain new and useful Improvements in Induction- Motors, of which the following is a full, clear, and exact specification.

My invention relates to induction motors.

In starting induction motors there is developed in the secondary circuit an electromotive force which is very high as compared with that developed when the motor is near synchronous speed. This is on account of the great slip' at starting. The tremendous current whichthis electro-motive force tends to produce in the winding of the secondary member reacts on the primary circuit and gives the motor a very low start ng torque. This large secondary current can be avoided or lessened by making the impedance of the secondary circuit greater while the motor is starting than while the motoris running near synchronism. This greater impedance during starting has been obtained in the case of wound rotor motors by putting a variable ohmic resistance in the secondary circuit and cutting out such resistance as the motor approaches synchronous speed.

It is the object of my present invention to provide an arrangement, which is particularly applicable to induction motors of the squirrel cage type, though it may also be used with motors of the wound rotor type, in which the secondary circuit has a higher impedance when the motor is starting-than when the motor is running, and in which the use of switching connections or sliding contacts is entirely avoided. This object is attained by partially o'r-wholly incasing the short-circuiting conductors of the secondary circuit with magnetic material. Since the fre quency of the current in the secondary circuit of an induction motor and the speed of such motor vary in inverse sense, it follows that becauseof this construction the shortcircuitin conductors have a greater reactance an the secondary circuit of the motor a greater impedance when the motor is starting thanwhen it is running at or near synchroni'sm. The reactance of these short-circuitingconductors and therefore the impedance of the secondary circuit gradually di- The various tion will appear from the description and drawings, and will be particularly pointed out in the claims.

Figure l is a partial longitudinal section of the rotor of an induction motor embodying my invention; Fig. 2 is a. partial end view of the rotor of Fig. 1; Fig. 3 is an onlarged section on the line 3-3 of Fig. 2. 4- and 5 are views corresponding to Figs. 1 and 2 respectively and show a modifica tion; Fig. 6 is an end view of an induction motor rotor showing a further modification; and Fig. 7 is a development of part of the magnetic shell of the modification of Fig. (i.

As usual, the rotor of the induction motor consists of a rotatable laminated core 10 in which are embedded the squirrel cage conductors 11, and the ends of the squirrel cage bars are all connected together by short-circuiting rings. But the short-circuiting rings, which may be made in a number of extend entirely around the rotor and are.

connected to one end of each of the squirrel cage bars 11, as by means of screws 13. The strips 12 are spaced from each other under each bar 11 by means of washers 14-, which are preferably made of iron. At intervals along the strips 12, and preferably between each bar. 11 and its neighbors, short strips 15 of magnetic material. preferably iron, are placed between the strips 12 and on the outside of the outer strips, .and the whole is wrapped around by a strip 16 also preferably of iron. The strip 16 forms a shell inclosing the strips 12 and 15. If desired, the iron strips 15 and 16 may be insulated; as by shellac, from the conducting strips. 12. By means of this construction each of the strips 12 is totally surrounded by iron between each pair of bars 11, and this magnetic shell around each strip 12 causes the reactance of the short-circuiting ring to be much larger at starting, when the frequency of the secondary circuit is high, than under running conditions, when such frequency is low. The impedance of the secondary circuit is therefore much higher when the motor is starting. than when it is running near synchronism, and therefore the large secondary currents and their reaction upon the primary circuit are avoided and t has an excellent startingtorque. tn the arrangement. shown in Fig 5, the shortcircuiting rings consist ol' t rality of metal strips to which the squirrel g cage bars 11 of the rotor are preferably i t riveted as shown. Such riveting may Well he :urcomplished by spinning over the end of each conductor ii. The alternate strips [7, preferably including the outside strips, are of iron or other magnetic material, and the remaining strips '18 are ol some good conducting material 'ifhc strips 17 and 18 may he insulated from each other as by shellac. ln this (JONStl'HCtltHl the strips LT form a practically complete magnetic shell around such strips 15%, and in r.:onscquence the SOC ondary circuit. of the motor has a comparatively high impedance at starting. As in the ar 'angement of Figs. 1, 2, and 3, in the arrangement of Figs. l and 5 the impedance gradually decreases as the speed of the motor increases.

in the arrangement shown in (1 and 7, the short-eircuiting rings each consist of a bar 19 of conducting material surrounded by a shell 90 of magnetic material. This shell is preferably cut away under the squirrel cage conductors lit, to allow the bar 19 to engage such conductors. The shell 20 may cmivenientlybc made of sheet iron, punched. in the form illustrated in Fig. 7 and bent on the dot and dash lines around the conducting bar 19 as shown in Fig.

\J. The shell 20 may be insulated from the bar 19, as by shellac. The short-circuiting rings in their entirety are fastened to the squirrel rage conductor bars 111. by means of screws 13, as in the arrangement of Figs. .1 and The magnetic. shells 20 around thecondueting bars l9-give the secondary circuit of the motor a comparatively high'impedance at starting, which impedance decreases as the motor approaches synchronous speed.

Other modifications may be made in. my invention without departing from its spirit tion motor, a core, a winding on the co and thereto.

and scope, and all such I aim. to cover in the tollowing claims.

What I claim as new is: l. in the secondary member of an inducshort-circuiting conductors at lc partly incased in iron carried by the wim mg.

2. In an induction motor rotor, a core, cpddrnwtor bars embedded in said core, shortcircuitmg rings connecting the ends 01" said bars, said rings consisting; of conducting 1: ix terial at least partially incascd in inagneuie maternal. I 3. in an. tinduetion motor rotor, a core, conductor bars embedded in said core, shortcircuitir rings connectingthe cruise? said conduc s, sald rings consistingof alternate.

strips of conducting and magnetic material.

at. In an induction motor rotor, 21 cor conductor bars embedded in said core, short circuiting rings connecting the ends of said conductor bars, said short. iting rinf comprising strips of conducting material he tween strips of magnetic material.

In an induction motor rotor, a core, conductor bars embedded in said core, shorteircuiting conductors conncctingthe ends of said bars, and shells or" magnetic material around and supported hysaid short-circ ing conductors.

6. In an induction motor rotor, a conductor liars embedded in said circuiting rings connecting tl 1e cnos ha s, said rings comprising a strips some of which are of m terial. Y

7. In an induction motor, a rotor core, squirrel cage bars therein, short-circuiting rings connecting corresponding ends of the bars, and magnetic material carried by the short-eircniting bars andin close proximity In testimony whereof I afii): my signature, in the presence of two witnesses.

CHARLES E. LORD.

Witnesses:

(jims ti. BYRON, Ros. l j'. S'roLL. 

